In particular the encasement is intended for the support column of an operating table. When the encasement needs to be replaced or access to the support column is needed for maintenance or repair, the annular elements of the encasement have to be opened. For this purpose the retainer clip has to be removed. In a known solution the rebates are provided with cuts close to their longitudinal ends which cuts extend perpendicularly to the longitudinal direction of the rebates so that when the retainer clip has been slid on, the lobes created by providing said cuts can be folded back behind the retainer clip towards the wall of the encasement element. There is a risk of damaging the exterior of the encasement element both when pushing the lobe against the wall of the encasement element and when bending the lobe away so as to again release the retainer clip.